Saturday, April 18, 2020
Mike Butler: Covid-19 model warnings flawedLabels: COVID-19, Ian Harrison, Mike Butler, Otago University, Te Punaha Matatini
The decision to lock down all “non-essential” workplaces was an overaction to a claim by modellers that between 8560 and 14,400 could die over the next year and that claim was not supported by evidence, Ian Harrison of Tailrisk Economics said today.
One model was built by the University of Otago Covid-19 Research Group and the other by Te Punaha Matatini, which is a cluster of researchers from Landcare Research and the Universities of Auckland and Canterbury.
Prime Minister Jacinda Ardern warned of 14,400 deaths after shutting down all “non-essential” workplaces for four weeks.
Harrison said “results depend on the most critical assumptions used by the modelers. To a degree modeling results can be what the modellers want them to be, so it is always critical that modellers clearly report their main assumptions and their impact on the results, upfront. They should not be hidden in the technical detail.”
University of Otago Covid-19 Research Group claims between 8560 and 14,400 could die over the next year if New Zealand fails with its current eradication strategy.
The Prime Minister has said that what prompted her to go quickly to the Level 4 intervention was a report showing some apparently extreme outcomes.
The Otago group used a simple online calculator but failed to use a key feature of the model that allows for contact tracing, testing and isolation.
Harrison found that the Otago model grossly overstated the number of deaths, because it assumed that there would be no tracing and isolation of cases, or, alternatively, that the Ministry was so ineffective that their efforts could be disregarded.
When Harrison ran the Otago Covidsim model he found credible paths that could reduce the pace of infections to sustainable levels. Deaths in the range of 50 to 500 over a year are more realistic numbers. The average level for seasonal flu deaths in New Zealand is around 500.
This Otago assumption that there would be no tracing and isolation of cases is almost incomprehensible, unless there was a deliberate attempt to blow up the numbers.
The more effective the case isolation process, the less the need for costly workplace closures, Harrison said.
Meanwhile the Te Punaha Matatini report, that purports to show that the Level 4 intervention was justified and suggests that it be extended, only looked at a comparison of the Level 2 and Level 4 interventions.
It did not consider the real question of whether some variant of a level three would be sufficient to contain the epidemic, he said.
Harrison, who has a BCA Hons. Victoria University of Wellington, and a Master of Public Policy at Johns Hopkins School of Advanced International Studies, has worked with the Reserve Bank of New Zealand, the World Bank, the International Monetary Fund, and the Bank for International Settlements.
The report titled “The Ministry of Health’s modelling of the impact of the Coronavirus on New Zealand: A look behind the headlines” may be read at http://www.tailrisk.co.nz/documentlist
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